In recent years, liquid crystal displays provided with a so-called environmental sensor (in the following, referred to as an “ambient sensor”) for detecting the intensity of ambient light (in the following, referred to as “external light”) have been known (for example, see Patent documents 1 and 2). In such liquid crystal displays, the intensity of light from backlight is adjusted according to the intensity of the detected external light.
More specifically, in the case of transparent liquid crystal displays, the light intensity of the backlight is raised in a bright environment such as the outdoors and reduced in a relatively dark environment such as the nighttime and indoors. Thus, the liquid crystal displays provided with the ambient sensor achieve improved screen visibility, lower power consumption and longer lifetime. The liquid crystal displays provided with the ambient sensor are useful particularly as a display device of portable terminals (for example, mobile phones, PDAs, hand-held game machine, etc.) that are often taken outdoors for use.
Examples of the ambient sensor include optical sensors such as a photodiode and a phototransistor. The optical sensor can be mounted on the liquid crystal display by placing an optical sensor provided as a discrete component on a display panel (for example, see Patent document 3). Also, in recent years, in order to cut the manufacturing cost and miniaturize the display device by reducing the number of components, an attempt has been made to form an optical sensor monolithically on an active matrix substrate constituting a display panel (for example, see Patent document 4). In this case, the optical sensor is formed by utilizing the process of forming an active element (TFT).
Herein, the configuration of a liquid crystal display on which an optical sensor is mounted will be described with reference to FIG. 5. FIG. 5 shows a schematic configuration of a conventional liquid crystal display on which an optical sensor is mounted. In FIG. 5, the configuration of a liquid crystal display panel constituting the liquid crystal display is illustrated schematically.
As shown in FIG. 5, the liquid crystal display panel is constituted by sandwiching a liquid crystal layer 102 between an active matrix substrate 101 and an opposed substrate 103. A region of the active matrix substrate 101 that is in contact with the liquid crystal layer 102 serves as a display region. In the display region, a plurality of pixels are arranged in matrix. The pixel includes an active element and a pixel electrode. Further, an optical sensor 104 is formed monolithically in a region surrounding the display region (in the following, referred to as a “peripheral region”) by utilizing the process of forming the active element.
A backlight is disposed on a back surface side (a side on which the active element is not formed) of the active matrix substrate 101. In the example of FIG. 5, the backlight is of a sidelight type and mainly includes a light guide plate 108 and a light source 105. The light source 105 is constituted by a fluorescent lamp 106 and a lamp reflector 107. Further, a reflective sheet 109 is attached to a lower surface and lateral surfaces (not shown) of the light guide plate 108. Moreover, a diffusing sheet 110 and a prism sheet 111 are attached to an upper surface (an emission surface) of the light guide plate 108 in this order.
Light emitted from the light source 105 is reflected inside the light guide plate 108 and emitted from the upper surface (the emission surface) of the light guide plate 108. The light emitted from the emission surface of the light guide plate 108 first enters the diffusing sheet 110 and is diffused. This reduces brightness unevenness. Further, the light that has passed through the diffusing sheet 110 is refracted by a prism sheet 111 so as to be turned into light that is substantially parallel with the normal to the emission surface, and passes through the active matrix substrate 101, the liquid crystal layer 102 and the opposed substrate 103 in this order.
Also, at this time, a control device of the backlight (not shown in FIG. 5) adjusts the intensity of light emitted from the light source 105 in the backlight according to the intensity of external light detected by the light sensor 104. Accordingly, using the liquid crystal display illustrated in FIG. 5, it is possible to improve the screen visibility and achieve lower power consumption and longer lifetime.
Patent document 1: JP 4 (1992)-174819 A
Patent document 2: JP 5 (1993)-241512 A
Patent document 3; JP 2002-62856 A (FIGS. 12 to 14)
Patent document 4: JP 2002-175026 A (FIG. 12)